golang解析x509证书(二进制)的扩展字段

package main

import (
    "crypto/x509"
    "flag"
    "fmt"
    "log"
    "os"
    "strconv"
)

var certname = flag.String("certname", "test.der", "input you certname")

func getCertInfo() {

    if len(os.Args) != 2 {
        log.Fatal("input certname....")
        return
    }
    flag.Parse()
    certCerFile, err := os.Open(*certname)

    if err != nil {
        log.Fatal(err)
    }
    derBytes := make([]byte, 1000)
    count, err := certCerFile.Read(derBytes)
    if err != nil {
        log.Fatal(err)
    }
    certCerFile.Close()
    cert, err := x509.ParseCertificate(derBytes[0:count])
    if err != nil {
        log.Fatal(err)
    }

    expiretime := strconv.FormatInt(cert.NotAfter.Unix(), 10)
    fmt.Printf(expiretime);
    extension := cert.Extensions

    if len(extension) > 0 {
        fmt.Printf(extension);
    }

}
func main() {
    getCertInfo()
}